Thin-film semiconductor device, manufacturing method of the same and image display apparatus

ABSTRACT

A method of forming thin-film semiconductor device is provided in which an island region of an isolated single-crystal thin-film is formed on an entire surface or within a specific region of an insulating film by utilizing cohesion phenomena due to the surface tension of a melted semiconductor, wherein more than one active region of a thin-film transistor is formed in the island region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin-film semiconductor device suchas a thin-film transistor (referred to as TFT hereinafter) made up of asemiconductor thin-film formed on an insulating substrate, amanufacturing method thereof, and an image display apparatus using sucha device.

2. Description of the Related Art

In recent years, as the amount of information in electronic data formincreases, the development of apparatus which processes and visuallydisplays such information is becoming more and more important. With anincrease in the size of image display apparatus and image sensors alongwith growth of the demand for higher integration density (higherprecision) of pixels, the use of TFTs capable of offering high-speeddrivability is required. To satisfy these requirements, it is inevitablyrequired to develop advanced technology which makes it possible tofabricate, at low costs, TFTs made of high-quality silicon (Si)thin-films on or above a low cost electrically insulating substrate,such as a large-size glass substrate or the like.

Conventionally, methods for crystallizing an amorphous Si thin-film areknown as high-quality Si thin-film fabrication technology. These methodsin turn involve a laser-aided crystallization technique, which has beenwidely employed until recently. For example, a Si thin-film crystallizedby use of an excimer laser is a polycrystalline silicon thin-film withits average grain size ranging from about 0.1 to 1.0 μm. In the case offabrication of a TFT of the metal oxide semiconductor (MOS) type, acrystal grain boundary inevitably exists within the channel region ofsuch a TFT. This results in a decrease in carrier mobility, which inturn leads to a degradation of performance.

Another problem faced with the approach is as follows. During fusioncrystallization, a difference in cubical or volume expansioncoefficients between a liquid Si and solid Si results in unwantedcreation of surface convex-concave irregularity at the grain boundary,causing the TFT to decrease in withstanding or breakdown voltage. Inview of these problems, a technique for enabling Si crystals to increasein grain diameter while at the same time offering surface planarizationcapabilities is strongly required.

As an example of a method of improving the performance of TFTs, anapparatus is disclosed, for example, JP-A-11-121753, which apparatuspermits crystals to grow to have an increased length in a specifieddirection while letting a source/drain layout direction (equivalent to acurrent flow direction) become almost identical to the elongatedirection of crystal grains thus grown. Additionally, in a liquidcrystal display device which is disclosed for example inJP-A-2000-243970 as an embodiment, the layout directions of the sourcesand drains of the TFTs are arranged to almost coincide with the elongatedirection of the crystal grains. Each TFT is disposed to have alongitudinal/lateral block shape (in a horizontal direction and in avertical direction) at a display pixel array peripheral portion, whenviewed from the surface side of an array substrate. However, since anyone of the TFTs is such that its channel region is notsingle-crystallized, the performance and reliability decrease by theinfluence of a trap level that exists at grain boundaries. This, inturn, causes a problem that the characteristics increase in variability.

Recently, crystallization technologies have been widely used whichemploy solid-state lasers (such as YAG laser or the like) extremelyhigher in beam stability than excimer lasers. However, while rectangularsingle-crystal grains are formed in a laser scan direction, the averagewidth thereof is merely from about 0.5 to 1.5 μm. Thus, it has beenimpossible to eliminate unwanted creation of grain boundaries within TFTactive regions. To be brief, the known approaches all suffer from thepresence of a plurality of grain boundaries within the active regions ofthe TFTs and also encounter a problem that the grain boundary number ineach TFT active region can vary. As a result, the TFT characteristicsare undesirably varied accordingly.

It is apparent from the technical problems stated above that in thefabrication technique for forming a high-quality polycrystalline film ona dielectric film by laser annealing methods, it remains difficult toform TFTs of high performance due to the lack of regularities of crystalgrain size and face orientation, and also due to difficulties in crystalgrain position control and others. Accordingly, in order to fabricate,by low-cost manufacturing methods, TFTs that are high in performance andreliability and yet low in variation, it is required tosingle-crystallize by relatively simple methods at least the activeregions of the TFTs on an insulating substrate.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide acrystallization technique for enabling a semiconductor thin-film tobecome a single-crystalline film without fail in a region for formationof a thin-film semiconductor device such as a thin-film transistor(TFT). Another object of this invention is to provide a thin-filmsemiconductor device capable of simultaneously achieving, by using thesemethods, improvements in performance of the TFT such as electric fieldeffect mobility and the like and also improvements in the uniformitythereof. A further object of the invention is to provide a manufacturingmethod of such thin-film semiconductor devices.

Through a variety of studies and experiments, the inventors haveconceived a thin-film semiconductor device, such as a TFT, capable ofsolving the problems stated above by using physical phenomena differentfrom traditional ones as well as a method for manufacturing such devicesand also an image display apparatus using the thin-film semiconductordevice of the present invention.

A first aspect of the invention lies in (1) a thin-film semiconductordevice which has an insulating substrate, and an island region of anisolated single-crystal thin-film as provided on or above the insulatingsubstrate.

(2) A further aspect is that the island region of the single-crystalthin-film has a cross-section perpendicular to the substrate, whereinthe cross-section is made up of a substantially circular shape, asubstantially elliptical shape or part of these shapes.

In addition, (3) the island region of the single-crystal thin-film is astripe-shaped single-crystal thin-film, and it is possible to form morethan one active region of a thin-film transistor within the islandregion of the single-crystal thin-film.

(4) The source/drain direction of the above-noted thin-film transistorcan be disposed substantially in parallel with or substantiallyperpendicular to the elongate direction of the stripe-shapedsingle-crystal thin-film. Note here that an example of the thin-filmtransistor is a field effect transistor.

Additionally, (5) at least one thin-film which corresponds to thestripe-shaped single-crystal thin-film stated above can be includedwithin the active region of the thin-film transistor.

Additionally, (6) it is possible to form at least more than one regioncorresponding to the active region of the thin-film transistor in thestripe-shaped single-crystal thin-film.

Additionally, (7) a main crystal orientation of the island region of thesingle-crystal thin-film that is provided above the insulating substratein a vertical direction relative to the substrate may be <110>, <100>or<111>, and a crystal orientation which is in a horizontal direction withrespect to the substrate and is the elongate direction of the islandregion of the single-crystal thin-film may be <110>, <100>or <111>.

A second aspect of the invention lies in (8) a manufacturing method of athin-film semiconductor device, which method has: a first step offorming a semiconductor thin-film on an insulating substrate andperforming patterning of the semiconductor thin-film; a second step ofpatterning a plurality of materials different in surface tension anddisposing patterned materials at an upper part or a lower part of thesemiconductor thin-film; a third step of melting the semiconductorthin-film by laser scanning and utilizing cohesion phenomena due to itssurface tension to perform position control in such a way as to performpositional alignment with a patterned position to thereby form an islandregion of an isolated single-crystal thin-film above the insulatingsubstrate; and a fourth step of forming more than one active region of athin-film transistor in the island region of the isolated single-crystalthin-film.

A third aspect of the invention lies in (9) an image display apparatuswhich includes an image display unit, a peripheral region thereof, and athin-film semiconductor device that is provided at least in theperipheral region of the image display unit and has an insulatingsubstrate and an island region of an isolated single-crystal thin-filmas provided above the insulating substrate, wherein the thin-filmsemi-conductor device includes at least one circuit used to drive theimage display apparatus, which circuit is selected from a groupconsisting of a buffer circuit, a sampling switch circuit, a prechargecircuit, a shift register circuit, a decoder circuit, a clock waveformreshaping circuit, a digital-to-analog converter circuit, a power supplyconversion circuit, a level shift circuit, a timing control circuit, anamplifier circuit, a memory, a processor, a gate array and acommunication circuit.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are representative drawings of the present invention andare diagrams each showing the form of a structure having asingle-crystal semiconductor thin-film which is formed on an insulatingsubstrate and a TFT as formed thereon.

FIGS. 2A to 2D illustrate some major process steps in the fabrication ofa single-crystal semiconductor thin-film on an insulating substrate.

FIGS. 3A and 3B are diagrams each showing the shape and crystallinity ofa single-crystal Si thin-film as formed on an insulating substrate.

FIGS. 4A to 4G are process diagrams showing steps in the fabrication ofa single-crystal semiconductor thin-film on an insulating substrate.

FIGS. 5A to 5E are process diagrams showing steps in the fabrication ofa single-crystal semiconductor thin-film on an insulating substrate.

FIGS. 6A to 6D are diagrams each showing a cross-sectional view of asingle-crystal semiconductor thin-film as formed on an insulatingsubstrate.

FIGS. 7A and 7B are diagrams showing the crystal surface orientation ofa single-crystal Si thin-film formed on an insulating substrate.

FIGS. 8A to 8E are diagrams each showing a thin-film semiconductordevice using a single-crystal semiconductor thin-film formed on aninsulating substrate.

FIGS. 9A and 9B are plan views schematically showing an arrangement ofan image display apparatus using a thin-film semiconductor device.

FIGS. 10A to 10D are diagrams each showing electronic equipment to whichthe image display apparatus of the invention is applied.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be explained with reference to theaccompanying drawings below. Note that although silicon (Si) is used asan example of the semiconductor material in the embodiments below forsimplification purposes only, similar effects of this invention areobtainable with respect to thin-films made of all possible IV-groupmaterials (i.e. any one of C, Si, Ge, Sn and Pb or mixed crystals ofthem).

Embodiment 1

An explanation will be given of a thin-film semiconductor device formedwith a single-crystalline Si thin-film after crystallization of asemiconductor thin film stacked on a substrate.

FIG. 1A shows a structure in which an underlay film 102 is formed on aninsulating substrate 101 on which a crystal grain 103 ofsingle-crystalline Si is formed.

FIG. 1B shows a TFT in which an insulating film 104 is formed on thesingle crystal grain 103 on which a source electrode 105, a gateelectrode 106 and a drain electrode 107 are formed.

FIG. 2A is a cross-sectional diagram in accordance with this embodiment.As shown herein, on an insulating substrate 201, an underlay film 202comprised of a Si oxide film with a thickness of about 100 nm, by way ofexample, and an amorphous Si thin-film 203 with its thickness of about50 to 200 nm, or more or less, are deposited by chemical vapordeposition (CVD) methods. In this case, the thickness of such amorphousSi thin-film and that of its underlying Si oxide film should not belimited only to the values presented in this embodiment. In addition,the arrangement of the underlay film 202 may alternatively be either aSi nitride film or a laminate or “multilayered” film of a Si nitridefilm and a Si nitride film. Thereafter, as shown in FIGS. 2B and 2C,laser scanning is done to perform crystallization of the amorphous Sithin-film 203, thereby forming a single-crystalline Si thin-film 204.FIG. 2D depicts a cross-sectional shape of single-crystal Si thin-film204 on the plane perpendicular to the laser scanning direction. At thistime, the amorphous Si film 203 is melted or fused by laser irradiation.The result is that a plurality of stripe-shaped single-crystal filmcomponents are formed by aggregation or cohesion due to surface tension.Each single-crystal film has a cross-sectional structure which is formedof a part of a cross sectional elliptical shape or cross sectionalcircular shape. Although in this embodiment, the laser scanning is donein a fixed direction by using a solid-state laser, there are no specificlimits as to the type of laser being used. Additionally, it is alsopossible to form the intended single-crystal thin-film by use ofwavelength-different lasers in combination. An example of this approachis as follows. First, the Si thin-film 203 is polycrystallized byexcimer laser scan techniques, and, thereafter, performed by scanningwith use of a solid-state laser.

FIGS. 3A and 3B are diagrams showing the features of a single-crystal Sithin-film which was formed by this crystallization method, wherein FIG.3A shows a picture image obtained by a scanning electron microscope(SEM), and FIG. 3B shows a bright field image (left side) of atransmission electron microscope (TEM) along with a dark field image(right side) thereof. It would be readily seen from viewing FIG. 3A thatstripe-shaped single-crystal Si thin-films 204 are formed on theinsulating substrate, which films extend in the same direction as thelaser scan direction. As shown in an inset of FIG. 3A, thesestripe-shaped single-crystal Si thin-films 204 are featured in that across-sectional structure on the plane perpendicular to the elongatedirection resembles a part of cross sectional elliptical shape or crosssectional circular shape. This is because Si as melted by laser scanningundergoes aggregation and condensation, or cohesion, due to surfacetension. In addition, crystals grow in a lateral direction by the laserscanning. This results in growth of a stripe-like single-crystal Sithin-film with a round sectional shape. Additionally, it is seen fromthe bright field image (left) shown in FIG. 3B that grain boundarieswhich would otherwise occur in conventional polycrystalline Sithin-films are no longer observed inside the crystal film. It is alsoseen from the dark field image (right) that each remains as asingle-crystal film with no grain boundaries or no defects beingcontained therein. In other words, the Si thin-films as formed in thisembodiment are stripe-like single-crystal Si thin-films formed on thesubstrate. Another feature lies in that the cross-sectional structure atthe plane at right angles to the elongate direction of the crystal filmshas a shape of part of either a circle or an ellipse.

Embodiment 2

In this embodiment 2, an explanation will be given of an embodimentwhich forms a single-crystal Si thin-film at a specified location on thedielectric substrate at the crystallization process step using laserscan techniques as has been set forth in the embodiment 1. That is, inthis embodiment an initial thin-film is patterned prior tocrystallization for position control of the single-crystal Si thin-film,and a single-crystal Si thin-film is formed while simultaneouslyperforming the position control by utilizing underlay films differentfrom each other in wettability with respect to the melted Si.

FIGS. 4A to 4G are diagrams for explanation of an embodiment which formsa single-crystal film by laser irradiation after having patterned anamorphous Si thin-film 203 into a variety of shapes. Firstly, as shownin FIG. 4A, an underlay film 202 and amorphous Si thin-film 203 areformed on a dielectric substrate 201. Then, as shown in FIG. 4B, withuse of resist deposition, photomask exposure, development and etchingprocesses, stripe-shaped regions of the amorphous Si film 203 with awidth of more 5 μm or less are periodically formed on the entire surfaceof the insulating substrate with 10 μm intervals, and the stripe-likeamorphous Si films 203 are thereafter crystallized by laser scanning.Use of this method makes it possible to periodically form thesingle-crystal Si thin-films having the same width and length on theoverall surface area.

Another embodiment of the method for performing patterning of theamorphous Si thin-film 203 prior to execution of the laser scanning isas follows. As shown in FIG. 4C, rectangular openings or holes 205 areformed by partial removal of the amorphous Si film on both sides of aregion to be single-crystallized. Then, as shown in FIG. 4D, thicknessof the rectangular amorphous Si film 206 of the source/drain regions ismade thicker than that of the channel regions. Furthermore, otherrectangular holes are formed on both sides of each TFT channel region.Next, as shown in FIG. 4E, the width of the source/drain region of TFTis made larger than that of the channel region, which defines apatterning of island regions having such shape of the width. Then asshown in FIG. 4F or 4G, after completion of patterning into aprespecified shape such as a circle or a square, and the crystallizationis performed, it then becomes possible to perform position control ofthe single-crystal films and the island regions thereof. Note here thatthe width, interval and length of the patterns shown in FIG. 4A to 4Gmay be modified in a variety of ways. Also, note that the regions to bepatterned may alternatively be the entire surface area of the insulatingsubstrate. As another alternative, the patterning may be done only atspecific locations for formation of high-performance TFTs.

FIGS. 5A to 5E are diagrams for explanation of another embodiment whichis designed to perform the position control of the island regions of asingle-crystal film by utilizing films which are different inwettability relative to a melted Si as the underlay film of Si film. Asshown in FIG. 5A, after having placed two kinds of films 207, 208 whichare different in wettability from each other under an amorphous Sithin-film 203, a laser scanning operation is performed. By virtue ofthis, as shown in FIG. 5B, a melt Si is condensed andsingle-crystallized on the film 207 of large wettability with respect toSi. Thus, it becomes possible to control the positions of island regions204 of single-crystal Si film. Although, in this embodiment, thewettability-different films are formed beneath the amorphous Sithin-film 203, another method is available, which is as follows. Awettability-strong film 207 may be formed beneath the amorphous Si filmwhile letting a wettability-weak film 208 be formed on the side faces ofisland regions 204 of a patterned amorphous Si film. Optionally, it isalso permissible to dispose wettability-different films on the amorphousSi thin-film 203. In addition, as shown in FIG. 5C, thewettability-strong film 207 is formed on an entire surface of thesubstrate on which an island pattern of the wettability-weak film 208 isdisposed, and the amorphous Si thin-film 203 is formed on thewettability-weak film on its overall surface area. Thereafter, whencrystallization by the laser scanning takes place, it is possible toform the island regions 204 of single-crystal film in such a manner thateach is between adjacent ones of the wettability-weak patterns 208, asshown in FIG. 5D. A thin-film semiconductor device may be formed in thesingle-crystal film island regions 204. It is also permissible to formsuch a thin-film semiconductor device after having removed the film 208as shown in FIG. 5E.

FIGS. 6A to 6D are diagrams each showing the features in cross-sectionalshape of a single-crystal Si thin-film island region as formed on aninsulating substrate. As shown in FIG. 6A, the cross-sectional shape ofthe single-crystal film island region thus formed in this embodiment isdefinable by the crystal cross-section's width (W), film thickness (H),curvature radius (R), and contact angle (θ) relative to the substrate.These parameters are determined depending upon the film thickness of athin-film semiconductor on the insulating substrate, the patterningscheme used, the wettability with respect to an Si thin-film, thesurface tension of an Si thin-film, the kind of laser, and the scanningmethod used. One example is that laser-scanning single-crystallizationis performed by use of a specimen having an amorphous Si film which is50 nm thick, thus obtaining a stripe-shaped single-crystal thin-filmwith W being equal to about 1.0 μm, H equal to about 100 nm, and θ ofabout 30°, while having a length of 100 μm, more or less. Note thatthese values are not the values limited to this embodiment, and it isalso possible to obtain single-crystal thin-film island regions withfurther greater areas by modifying the film thickness of amorphous Siand the energy of laser irradiation and others in a variety of ways.Also note that adequately designing the materials of thewettability-different films and the patterning shapes makes it possibleto form, on the insulating substrate, single-crystal film island regionswith various cross-sectional shapes as shown in FIGS. 6B to 6D.

Reference is now made to FIGS. 7A and 7B. FIG. 7A (upper part) is adiagram for explanation of the crystal plane/surface orientationobtained as a result of analysis using electron diffraction methods, inthe stripe-shaped single-crystal Si thin-film thus formed in thisembodiment. FIG. 7B shows a table indicating crystal orientations in avertical direction with respect to respective crystal surfaces. Upondetermination of the crystal surface orientations by means of electrondiffraction methods, the direction of an incoming electron beam issubstantially at right angles to the substrate. Additionally, although aneed is felt to let the specimen of interest be inclined or tiltedwithin an angular range of ±5° with respect to the electron beam'sincident direction in order to obtain the optimal crystal surfaceorientation, such tilting within this angular range hardly affects thedetermination of the crystal surface orientation. The actual analysisresults demonstrate that the crystal surface orientation in a verticaldirection to the substrate (i.e., V-direction) is <110>at more than 90%of all measurement points, with the others exhibiting the presence of<100>and <111>or else at random. In short, this indicates that the mainorientation of the single-crystal thin-film thus formed in thisembodiment in the vertical direction relative to the substrate is <110>.Additionally, the surface direction in cross-section of thestripe-shaped single-crystal thin-film was analyzed by an electrondiffraction method to reveal the fact that the surface orientation of astripe shape in the laser scan direction, that is, in the elongatedirection thereof (L-direction), is such that <100>is the mainorientation. FIG. 7B shows the crystal orientation in the L-directionwith respect to the crystal orientation in the V-direction, noting thatthe L-direction refers to the laser scanning direction. For example,when the V-direction is <100>, the L-direction at right angles theretobecomes the direction <100>or <110>or <111>.

As is apparent from the foregoing discussion, the use of the method forpatterning the initial thin-film prior to single-crystallization bymeans of laser scanning makes it possible to form the intended islandregion of single-crystal Si thin-film at a specific location. It is alsopossible to further enhance the surface tension effects. Thus, itbecomes possible to successfully form a single-crystal Si thin-film ofhigh quality. It must be noted that although the patterning is appliedto the amorphous Si thin-film in this embodiment, an alternativeapproach is available as another embodiment which follows. The amorphousSi thin-film is polycrystallized by an excimer laser or the like. Then,the resultant poly-Si thin film is patterned. Thereafter, thesingle-crystallization may be performed by using a solid-state laser orsimilar device. Optionally, the process of fabricating an amorphous Sithin-film on the insulating substrate as the initial Si thin-film priorto laser scanning may be replaced with a process of fabricating thepoly-Si thin-film by using, for example, either a low-temperature CVDmethod using catalysts, also known as the catalytic CVD or “Cat-CVD”method, or a substrate heatup CVD method. Furthermore, it is alsopossible to perform laser-scanning single-crystallization after havingpatterned the poly-Si thin-film that was fabricated by these CVDmethods.

Embodiment 3

This embodiment is an example which forms a thin-film semiconductordevice at the single-crystal thin-film 204 which was formed by themanufacturing methods as has been explained in the above-notedembodiments 1 and 2. Its device structure and manufacturing method willbe explained with reference to FIGS. 8A to 8E.

FIG. 8A depicts a stripe-shaped single-crystal Si thin-film 204 which isformed on an insulating substrate, wherein its elongate direction isindicated by dotted line A and its vertical direction is by dotted lineB. FIG. 8B is a diagram for explanation of the cross-sectional structureof a MOS-TFT as formed at the stripe-shaped single-crystal Si thin-filmshown in FIG. 8A, wherein the source/drain direction is identical to theelongate direction (direction A). A drawing on the left side shows asectional structure as taken along the line A. A gate insulating film301, also known as gate insulator film, is formed on the single-crystalSi film 204. Then, source/drain-use contact holes 302, 303 are formedalong with electrodes 304-305, a gate electrode 306 and an insulatingfilm 307. In addition, a cross-sectional structure taken along line C,which is depicted to pass through the center of the gate, is shown onthe right side. A main feature lies in that the TFT's channel region isformed in the single-crystal Si film 204 with a cross-sectional shaperesembling an ellipse.

FIG. 8C is a drawing which shows a cross-sectional structure of a TFTwith its source and drain disposed in a direction (direction B) which isperpendicular to the elongate direction of the stripe-shapedsingle-crystal film 204 shown in FIG. 8A. In this embodiment the gateelectrode 306 is specifically laid out so that it extends in theelongate direction (direction A) of the stripe-like single-crystal Sithin-film 204. Thus, it becomes possible to increase the gate width,which in turn makes it possible to enhance the current drivingcapability of the TFT.

Additionally, FIG. 8D shows an exemplary TFT with its channel made up ofa plurality of stripe-shaped single-crystal Si thin-films, each of whichcorresponds to the stripe-shaped single-crystal Si thin-film 204 statedsupra. Although this TFT is arranged so that the contact holes of itssource and drain are formed in each stripe-shaped single-crystal Sithin-film, it is also possible, as shown in the drawing, to processeither a Si film being formed on the same surface of the single-crystalSi thin-film 204 or Si films, which are formed as separate layers, oneof which overlies the single-crystal Si film 204 and the other of whichunderlies the same, in such a way that each has a rectangular shape.Contact holes 302 and 303 are then provided in the rectangular Si films320 and 321. With such an arrangement, it was possible to suppress anunwanted cutaway of an underlay film of the single-crystal Si thin-film204 which would otherwise occur due to over-etching at the time ofopening of such contact holes. This in turn makes it possible tofabricate TFTs with increased stability and reliability. Additionally,although the case of a single gate is shown herein, it is also possibleto employ a TFT structure having a plurality of gate electrodes.

It is also possible to form a TFT by micromachining the single-crystalfilm 204 using isotropic etch techniques prior to formation of the TFTto thereby change the cross-sectional shape into either a circle orellipse.

FIG. 8E is a diagram for explanation of an embodiment with a pluralityof TFTs 310 formed on the single-crystal Si film 204 stated above. Inthis embodiment, a rectangular single-crystal Si thin-film 204 is formedso that its area measures about 5 μm×20 μm. Then, TFTs are formed by useof microfabrication techniques with the minimum feature size of more orless 0.1 μm. The layout of these TFTs and the source/drain direction orthe like may be modified in a variety of ways when the need arises. Inthis way, it was possible to fabricate a plurality of thin-filmsemiconductor devices such as TFTs each formed of a single-crystal Sithin-film, thus enabling achievement of an integrated circuit.

As another embodiment, it was also possible to form TFTs by using laserscanning of single-crystallized island regions of an amorphous Si filmas patterned, for example, into the shapes shown in FIGS. 4D-4E and thenproviding source/drain regions and gates in such single-crystalthin-film island regions.

In the way stated above, it was possible to realize the TFTs formed of asingle-crystal Si thin-film on the insulating substrate by using arelatively simple and easy method with reduced process complexities. Asthese TFTs are high in performance and reliability and yet low in riskof variability in characteristics, it is possible by use of these TFTsto form large-scale integrated circuitry, formed on a conventionalsingle-crystalline Si substrate, or on a quartz glass substrate which isan almost perfect insulating film substrate. Further, it is possible toform an image display apparatus with built-in circuitry on a large-areaand low-cost glass substrate.

Although this embodiment is an example with formation of MOS-TFTs, it isalso possible to form devices of different structures including, but notlimited to, bipolar transistors and diodes other than the MOSTFTs, whiletaking full advantage of the film obtainable by the present invention,which is a single-crystal Si thin-film of high quality.

Embodiment 4

An explanation will next be given of an embodiment which employs, in animage display apparatus, thin-film semiconductor devices comprising thesingle-crystal Si thin-films shown in the above-discussed embodiments1-3, with reference to schematic plan views of FIGS. 9A and 9B.

This embodiment is a so called system-on panel which mounts, on the samesubstrate, both an image display device made up of liquid crystal ororganic electro-luminescence (EL) and its associative system componentsfor driving it. These associative system components include, but are notlimited to, a driver circuit, a digital-to-analog converter (DAC)circuit, a power supply circuit, a logic circuit, and a frame memory.These circuits are made up of TFTs incorporating the principles of thisinvention. In light of the fact that the TFTs are formed on the sameglass substrate, the manufacturing process temperature was set at 500°C. or below, by way of example.

An explanation of the manufacturing process of such TFTs is as follows.First, as shown in FIG. 9A, an amorphous Si thin-film 203 is depositedon a large-size/low-cost insulating substrate 201 made, for example, ofglass or plastic material. Then, an entire surface of the substrate isscanned by an excimer laser which is a first laser step to form apolycrystalline Si thin-film. Next, patterning is performed on thepoly-Si thin-film, as required, for a region 401 at peripheral portionsof a display pixel array in which necessary circuits are formed, such asa driver circuit, a digital-to-analog converter circuit, a power supplycircuit, a logic circuit, a frame memory and others. Again, laserscanning, such as a solid-state laser, is applied thereto as a secondlaser step, thereby forming TFTs comprised of a single-crystal Sithin-film within the region 401 by the method of the invention andforming the necessary circuitry.

Although the above-noted crystallization process is designed tocrystallize the entire substrate surface by an excimer laser and thensingle-crystallized for only the peripheral circuit region 401 byre-execution of the laser scanning, similar results are also obtainableby other methods. For instance, it is also possible to form the pixelbuilt-in circuitry such as pixel TFTs and pixel memories or the like bya method having the steps of depositing an amorphous Si thin-film,single-crystallizing it by overall-surface laser scanning, forming TFTscomprised of a single-crystal Si thin-film not only in the peripheralcircuit region but also in the display pixel array unit, and thenforming the pixel built-in circuitry such as pixel TFTs and pixelmemories. Optionally, in order to maximally eliminate laser scanningsteps, the single-crystal Si thin-film TFTs may also be formed bydepositing a poly-Si thin-film on the entire surface by low-temperatureCVD methods, for example, and thereafter selectively laser-scanning onlyspecified locations of the peripheral circuit region where the TFTs areto be formed.

FIG. 9B is a schematic plan view of an apparatus configuration of asystem-on panel using the TFTs as formed by the manufacturing processstated above. At the periphery of an image display unit 410,high-performance TFTs formed of a single-crystal Si thin-film areprovided to thereby make up peripheral circuits such as circuitry 411with a frame memory and an image/video signal driver included therein, avertical scanning circuit 412, a logic circuit 413, an interface circuit414, a power supply circuit 415, a DAC circuit 416 and others. Wiringleads 415 are used to connect between these peripheral circuits andpixel circuits, thus completing the system-on panel. Implementation ofthe invention enabled achievement of light weight and slim size ofsystem-on panels high in picture image quality and reliability and yetlow in power consumption.

Embodiment 5

This embodiment is electronic equipment employing the system-on panelshown in the above embodiment 4. Some preferred forms of it are shown inFIGS. 10A to 10D. Applicability is attained to various types ofelectronic equipment including, but not limited to, slim size oflarge-screen television (TV) sets, monitor units for use with personalcomputers (PCs), handheld wireless telephone handsets, and mobileinformation terminals such as personal digital assistant (PDA) tools.Very importantly, letting the peripheral circuits that have beenarranged by LSI chip mount schemes be built together on the samesubstrate while using the TFTs of the invention makes it possible toreduce production costs in addition to the features such as high imagequality, low power consumption, high reliability, reduced panelthickness, and light weight.

According to the present invention, it becomes possible to fabricate atlow temperatures the thin-film semiconductor devices such as TFTs formedof a single-crystal Si thin-film on an insulating substrate. This, inturn, makes it possible to realize image display apparatus with built-insystems (e.g. system-on panels) and also achieve integrated circuitry onan almost complete insulating substrate.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A manufacturing method of a thin-film semiconductor device, saidmethod comprising: a first step of forming a semiconductor thin-filmabove an insulating substrate and performing patterning of thesemiconductor thin-film; a second step of patterning a plurality ofmaterials different in surface tension and disposing resulting patternedmaterials at an upper part or a lower part of the semiconductorthin-film; a third step of melting the semiconductor thin-film byirradiating a laser beam onto the semiconductor thin-film and utilizingcohesion phenomena due to surface tension to perform position control insuch a way as to perform positional alignment with a patterned positionto thereby form an island region of an isolated single-crystal thin-filmabove said insulating substrate; and a fourth step of forming more thanone active region of a thin-film transistor in the island region of theisolated single-crystal thin-film.
 2. The manufacturing method of athin-film semiconductor device according to claim 1, wherein said islandregion of the single-crystal thin-film has a cross-section perpendicularto the substrate, the cross-section being comprised of a substantiallycircular shape, a substantially elliptical shape or part of theseshapes.
 3. The manufacturing method of a thin-film semiconductor deviceaccording to claim 1, wherein said island region of the single-crystalthin-film is a stripe-shaped single-crystal thin-film and wherein anactive region of a thin-film transistor is formed in the island regionof the single-crystal thin-film.
 4. The manufacturing method of athin-film semiconductor device according to claim 3, wherein asource/drain direction of said thin-film transistor is disposedsubstantially parallel with or substantially perpendicular to anelongate direction of said stripe-shaped single-crystal thin-film. 5.The manufacturing method of a thin-film semiconductor device accordingto claim 3, wherein at least one film corresponding to saidstripe-shaped single-crystal thin-film is included within the activeregion of said thin-film transistor.
 6. The manufacturing method of athin-film semiconductor device according to claim 3, wherein at leastmore than one region corresponding to the active region of saidthin-film transistor is formed in said stripe-shaped single-crystalthin-film.
 7. The manufacturing method of a thin-film semiconductordevice according to claim 1, wherein a main crystal orientation of saidisland region of the single-crystal thin-film provided above saidinsulating substrate in a vertical direction relative to the substrateis <110>, <100>or <111>, and wherein a crystal orientation being in ahorizontal direction with respect to the substrate and being an elongatedirection of said island region of the single-crystal thin-film is<110>, <100>or <111>.